This trial consists of two arms. One arm is a non pre-treatment arm. Participants in this arm will receive placebo immediately after NSTEMI diagnosis and prior to the diagnostic coronary angiography. A 60 mg prasugrel loading dose will be given immediately after coronary angiography when proceeding to PCI. Subsequently, participants will receive daily maintenance doses of prasugrel until day 30. Participants who are greater than or equal to 75 years of age or who have a body weight less than 60 kilograms (kg) will receive 5 mg oral dose daily. All others will receive a 10 mg oral daily maintenance dose for 30 days.